Abstract

The resistivity of Cr-doped -type single crystals has been investigated in the temperature interval of . The data are analyzed within the framework of the variable-range hopping (VRH) mechanism for both the Mott and the Shklovskii–Efros regimes. With decreasing temperature a crossover between the Mott and the Shklovskii–Efros VRH conductivity regimes is observed. It is shown that the temperature dependence of the resistivity, , of Cr-doped crystals, that follows a VRH conductivity mechanism, obeys a scaling law . The values of the characteristic and the transition temperatures , as well as the width of the soft Coulomb gap in the spectrum of the density of the localized states (DOS) are determined. The observed values of the VRH transition and characteristic temperatures indicate the existence of a rigid gap in the spectrum of the DOS in addition to . This points to the polaronic nature of the charge carriers in the investigated compound.